Daikin Altherma Heat Pump Error and Fault Codes Guide

Daikin Altherma heat pumps are renowned for their efficiency, reliability, and ability to deliver both heating and cooling solutions for homes and businesses. However, like any complex HVAC system, occasional faults may occur. These are displayed as Daikin Altherma error codes or fault codes on the unit’s control panel, offering a valuable diagnostic tool for homeowners and technicians alike. If you are reading this article then you are likely already the proud owner of an Altherma, but you might find our review of Daikin heat pumps useful to provide another perspective.

In this guide, we’ll break down the most common Daikin Altherma fault codes, explain their causes, and provide actionable troubleshooting tips to get your heat pump back in operation.

What Are Daikin Altherma Fault Codes?

Daikin Altherma heat pumps use a fault code system to identify and issues quickly. These error codes will typically appear on the controller panel / wiring centre, with each code identifying the specific problem, such as a sensor malfunction, communication error, or compressor overload and our guide will provide actions to take in order to resolve them. Many of the required actions will need a professional heating engineer or electrician.

Understanding these error codes will mean you can:

✔ Identify the issues quickly

✔ Reduce the downtime of the unit

✔ Avoid costly repairs via early intervention

The inside mechanics of a Daikin Altherma, it cover taken off

Common Daikin Altherma Fault Codes Explained

Below are some of the most common fault codes you might encounter on your Daikin Altherma heat pump:

A1 – Malfunction of Indoor Unit PCB: Inspect and replace the indoor PCB if faulty.

A3 – Drain Level Control System Abnormality: Clear drain blockages and ensure proper drainage slope.

C4 – Malfunction of Liquid Pipe Thermistor: Check thermistor connections and replace if needed.

E3 – Actuation of High-Pressure Switch: Clean outdoor heat exchanger and ensure proper water flow.

U0 – Low Refrigerant Level: Check refrigerant levels and repair any detected leaks.

For a complete list of Daikin Altherma fault codes, check the detailed table provided below.

Fault Code	Description	Possible Causes	Suggested Actions
A1	Malfunction of Indoor Unit PCB	Defective indoor unit PCB; external factors such as electrical noise.	Inspect and, if necessary, replace the indoor unit PCB; check for sources of electrical interference.
A3	Drain Level Control System Abnormality	Drain clogging or improper slope; defective drain pump or float switch.	Clear blockages; ensure proper drain installation; replace faulty components.
A5	High Pressure Protection	Insufficient water circulation; dirty heat exchanger; high ambient temperatures.	Ensure proper water flow; clean heat exchanger; reduce ambient temperature.
A6	Malfunction of Fan Motor	Broken wires, short circuits, or defective fan motor/indoor unit PCB.	Check wiring connections; test and replace the fan motor or PCB as needed.
C4	Malfunction of Liquid Pipe Thermistor	Defective thermistor; faulty indoor unit PCB; poor connector contact.	Inspect and replace the thermistor; ensure secure connections; evaluate the PCB.
C5	Malfunction of Heat Exchanger Thermistor	Poor connection; defective thermistor; PCB failure.	Inspect and secure connections; replace faulty thermistor; evaluate the PCB.
E1	Malfunction of Outdoor Unit PCB	Faulty outdoor unit PCB; electrical noise interference.	Inspect the outdoor PCB; replace if necessary; check for electrical interference.
E3	Actuation of High Pressure Switch (HPS)	Dirty outdoor heat exchanger; clogged refrigerant piping; poor water circulation.	Clean the heat exchanger; clear refrigerant piping; ensure sufficient water flow.
E4	Actuation of Low Pressure Switch (LPS)	Insufficient refrigerant; refrigerant leak; faulty LPS.	Check refrigerant levels; inspect for leaks; replace faulty LPS.
E5	Overcurrent Detected in Compressor	Inverter board failure; compressor issue.	Inspect the inverter board; verify compressor function; check wiring.
F3	Discharge Temperature Error	High compressor discharge temperature detected.	Check refrigerant levels; inspect compressor; ensure proper airflow.
H0	Malfunction of Outdoor Unit PCB	Faulty PCB; electrical noise interference.	Inspect outdoor PCB; replace if necessary; check electrical environment.
H1	Defrost Operation Failure	Ice buildup; sensor failure; environmental factors.	Inspect ice sensors; clear ice buildup; verify proper sensor operation.
H9	Outdoor Air Temperature Sensor Malfunction	Defective sensor; poor connection; PCB issue.	Check sensor resistance; replace if faulty; inspect PCB.
J3	Discharge Pipe Temperature Sensor Malfunction	Defective temperature sensor; poor connector contact; PCB malfunction.	Inspect and replace the temperature sensor; check connectors and PCB.
J5	Suction Pipe Temperature Sensor Malfunction	Faulty suction temperature sensor.	Inspect and replace suction temperature sensor; secure connections.
L0	Insufficient Water Flow	Water pump failure; airlock in system; blockage in water pipes.	Inspect water pump; bleed the system; clear obstructions.
L5	Current Protection Error	Abnormal current detected; wiring faults; inverter failure.	Inspect current flow; verify wiring; check inverter operation.
P4	High Discharge Temperature	Compressor overheating; refrigerant undercharge; poor airflow.	Inspect refrigerant charge; ensure proper ventilation and airflow.
U0	Low Refrigerant Level	Insufficient refrigerant; refrigerant leak detected.	Check refrigerant levels; locate and fix leaks; recharge refrigerant.
U1	Voltage Supply Error	Power supply voltage outside operational range.	Check mains power supply; inspect connections; stabilize power supply.
U4	Communication Error Between Indoor and Outdoor	Faulty wiring or poor connection between indoor and outdoor units.	Check and secure all wiring connections; restart the system.
U5	Malfunction of Inverter PCB	Inverter PCB error; incorrect power supply.	Inspect PCB; verify proper power supply; replace if faulty.
U8	Fan Motor Malfunction	Fan motor locked, wiring issue, or motor failure.	Check wiring; inspect fan motor operation; replace if required.
UA	Duplicate Address Error	Two devices on the network have the same address.	Verify and reset duplicate addresses; ensure each unit has a unique address.
H3	High Water Temperature Error	Overheated water detected in the system.	Check water circulation; inspect thermistor; verify pump operation.
L8	Indoor/Outdoor Mismatch Error	Indoor and outdoor units are incompatible.	Verify unit compatibility; consult system documentation for supported models.
F6	Compressor Overload	Excessive compressor load detected.	Inspect refrigerant levels; check compressor operation; clear blockages.

What are Daikin Altherma Error Messages

Follow the below steps to allow you to troubleshoot your Daikin Altherma heat pump:

✔ Check the Control Panel: Find and note the error or fault code that is displayed.

✔ Refer to the Fault Code Table in this Guide: Use our table, or your Daikin manual, to identify the issue.

✔ Inspect the Components: Look for any loose connections, leaks, or visible damage to the specified area or parts.

✔ Restart the System: Turn off the heat pump, wait a few minutes, and restart it.

✔ Get in Contact with a Professional: If the fault persists, or you are unsure of how to resolve the issue, then consult a qualified technician.

Proactive Maintenance Tips for Daikin Altherma Heat Pumps

Preventing a fault is often easier (and cheaper) than fixing it. Here are some key maintenance tips for you to follow as preventative measures:

Carry out Regular Inspections: Take out a Service Plan to schedule annual check-ups from a professional.

Monitor the Water Pressure: Ensure water pressure remains at recommended levels.

Keep the Outdoor Unit Clear: Remove any leaves, dirt, and / or obstructions from the outdoor unit.

Observe the System Performance: Listen out for unusual noises, check for reduced efficiency and / or increased energy consumption.

Frequently Asked Questions (FAQs)

Q: How do I reset my Mitsubishi Ecodan heat pump?
A: Turn off the unit, wait five minutes, and restart it. If the issue persists, consult a technician.

Q: What does L3 mean on a Mitsubishi Ecodan heat pump?
A: It indicates circulation water temperature overheat protection. Check for leaks, blockages, and water pump issues.

Q: How can I fix an E6 error on my Mitsubishi Ecodan?
A: Ensure both indoor and outdoor units are powered on. Inspect cables for damage or loose connections.

Q: Can I troubleshoot Mitsubishi Ecodan faults myself?
A: Simple faults, like checking for leaks or resetting the unit, can often be fixed at home. For complex issues, professional help is recommended.

Q: How can I prevent Mitsubishi Ecodan fault codes?
A: Schedule regular maintenance, monitor pressure levels, and ensure the outdoor unit remains clean.

Conclusion

Identifying and understanding the Daikin Altherma heat pump error codes can save both time and money, preventing minor issues from becoming expensive repairs, if acted upon quickly. Identifying the issue will help you determine whether it is something you can fix yourself, or if you need professional help. If the unit is quite old, outside of the warranty and it starting to have faults more regularly then try our online quote tool to find a suitable replacement. Replacing an existing heat pump is much easier and cheaper than the initial install. Arrange a call with our team to discuss the process of replacing a heat pump.

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